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Cherednichenko, S., Kroug, M., Merkel, H., Kollberg, E., Loudkov, D., Smirnov, K., et al. (2001). Local oscillator power requirement and saturation effects in NbN HEB mixers. In C. Iit.u.t.e of T. Jet Propulsion Laboratory (Ed.), Proc. 12th Int. Symp. Space Terahertz Technol. (pp. 273–285). San Diego, CA, USA.
Abstract: The local oscillator power required for NbN hot-electron bolometric mixers (P LO ) was investigated with respect to mixer size, critical temperature and ambient temperature. P LO can be decreased by a factor of 10 as the mixer size decreases from 4×0.4 µm 2 to 0.6×0.13 µm 2 . For the smallest volume mixer the optimal local oscillator power was found to be 15 nW. We found that for such mixer no signal compression was observed up to an input signal of 2 nW which corresponds to an equivalent input load of 20,000 K. For a constant mixer volume, reduction of T c can decrease optimal local oscillator power at least by a factor of 2 without a deterioration of the receiver noise temperature. Bath temperature was found to have minor effect on the receiver characteristics.
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Kroug, M., Cherednichenko, S., Choumas, M., Merkel, H., Kollberg, E., Hübers, H. - W., et al. (2001). HEB quasi-optical heterodyne receiver for THz frequencies. In Proc. 12th Int. Symp. Space Terahertz Technol. (pp. 244–252). San Diego, CA, USA.
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Merkel, H. F., Khosropanah, P., Sigfrid Yngvesson, K., Cherednichenko, S., Kroug, M., Adam, A., et al. (2001). An active zone small signal model for hot-electron bolometric mixers. In Proc. 12th Int. Symp. Space Terahertz Technol. (55). San Diego, CA, USA.
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Cherednichenko, S., Kroug, M., Khosropanah, P., Adam, A., Merkel, H., Kolberg, E., et al. (2002). A broadband terahertz heterodyne receiver with an NbN HEB mixer. In Harward University (Ed.), Proc. 13th Int. Symp. Space Terahertz Technol. (pp. 85–95). Cambridge, MA, USA.
Abstract: We present a broadband and low noise heterodyne receiver for 1.4-1.7 THz designed for the Hershel Space Observatory. A phonon- cooled NbN HEB mixer was integrated with a normal metal double- slot antenna and an elliptical silicon lens. DSB receiver noise temperature Tr was measured from 1 GHz through 8GHz intermediate frequency band with 50 MHz instantaneous bandwidth. At 4.2 K bath temperature and at 1.6 THz LO frequency Tr is 800 K with the receiver noise bandwidth of 5 GHz. While at 2 K bath temperature Tr was as low as 700 K. At 0.6 THz and 1.1 THz a spiral antenna integrated NbN HEB mixer showed the receiver noise temperature 500 K and 800 K, though no antireflection coating was used in this case. Tr of 1100 K was achieved at 2.5 THz while the receiver noise bandwidth was 4 GHz.
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Uzawa, Y., Kojima, T., Kroug, M., Takeda, M., Candotti, M., Fujii, Y., et al. (2009). Development of the 787-950 GHz ALMA band 10 cartridge. In Proc. 20th Int. Symp. Space Terahertz Technol. (p. 12).
Abstract: We are developing the Atacama Large Millimeter/Submillimeter Array (ALMA) Band 10 (787-950 GHz) receiver cartridge. The incoming beam from the 12-m antenna is reflected by a pair of two ellipsoidal mirrors placed in the cartridge, and then split into two orthogonal polarizations by a free-standing wire-grid. Each beam enters a corrugated feed horn attached to a double-side-band (DSB) mixer block. The mixer uses a full-height waveguide and an NbTiN- or NbN-based superconductor-insulator-superconductor (SIS) mixer chip. We are testing the following three types of mixer chips: 1) Nb SIS junctions + NbTiN/SiO2/Al tuning circuits on a quartz substrate, 2) Nb SIS junctions + NbN/SiO2/Al tuning circuits on an MgO substrate, and 3) NbN SIS junctions + NbN or NbTiN tuning circuits on an MgO substrate. The IF system uses a 4-12-GHz cooled low-noise InP-based MMIC amplifier developed by Caltech. So far, the type 1) has shown the best performance. At LO frequencies from 800 to 940 GHz, the mixer noise temperatures measured by using the standard Y-factor method were below 240 K at an operating physical temperature of 4 K. The lowest noise temperature, 169 K, was obtained at the center frequency of the band 10, as designed. These well-developed technologies will be implemented in the band 10 cartridge to achieve the ALMA specifications.
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Merkel, H. F., Yagoubov, P. A., Kroug, M., Khosropanah, P., Kollberg, E. L., Gol’tsman, G. N., et al. (1998). Noise temperature and absorbed LO power measurement methods for NbN phonon-cooled hot electron bolometric mixers at terahertz frequencies. In Proc. 28th European Microwave Conf. (Vol. 1, pp. 294–299).
Abstract: In this paper the absorbed LO power requirements and the noise performance of NbN based phonon-cooled hot electron bolometric (HEB) quasioptical mixers are investigated for RF frequencies in the 0.55-1.1 range The minimal measured DSB noise temperatures are about 500 K at 640 GHz, 600 K at 750 GHz, 850 K at 910 GHz and 1250 K at 1.1 THz. The increase in noise temperature at 1.1THz is attributed to water absorption. The absorbed LO power is measured using a calorimetric approach. The results are subsequently corrected for lattice heating. These values are compared to results of a novel one dimensional hot spot mixer models and to a more traditional isotherm method which tends to underestimate the absorbed LO power for small bias powers. Typically a LO power between 50nW and 100nW is needed to pump the device to the optimal operating point.
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Ekström, H., Kroug, M., Belitsky, V., Kollberg, E., Olsson, H., Goltsman, G., et al. (1996). Hot electron mixers for THz applications. In E. J. Rolfe, & G. Pilbratt (Eds.), Proc. 30th ESLAB (pp. 207–210).
Abstract: We have measured the noise performance of 35 A thin NbN HEB devices integrated with spiral antennas on antireflection coated silicon substrate lenses at 620 GHz. From the noise measurements we have determined a total conversion gain of the receiver of—16 dB, and an intrinsic conversion of about-10 dB. The IF bandwidth of the 35 A thick NbN devices is at least 3 GHz. The DSB receiver noise temperature is less than 1450 K. Without mismatch losses, which is possible to obtain with a shorter device, and with reduced loss from the beamsplitter, we expect to achieve a DSB receiver noise temperature of less ‘than 700 K.
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Yagoubov, P., Kroug, M., Merkel, H., Kollberg, E., Schubert, J., Hubers, H. - W., et al. (1998). Performance of NbN phonon-cooled hot-electron bolometric mixer at Terahertz frequencies. In Proc. 6-th Int. Conf. Terahertz Electron. (pp. 149–152).
Abstract: The performance of a NbN based phonon-cooled Hot Electron Bolometric (HEB) quasioptical mixer is investigated in the 0.65-3.12 THz frequency range. The device is made from a 3 nm thick NbN film on high resistivity Si and integrated with a planar spiral antenna on the same substrate. The in-plane dimensions of the bolometer strip are 0.2/spl times/2 /spl mu/m. The results of the DSB noire temperature are: 1300 K at 650 GHz, 4700 K at 2.5 TBz and 10000 K at 3.12 THz. The RF bandwidth of the receiver is at least 2.5 THz. The amount of LO power absorbed in the bolometer is about 100 nW. The mixer is linear to within 1 dB compression up to the signal level 10 dB below that of the LO. The intrinsic single sideband conversion gain is measured to be -9 dB, the total conversion gain -14 dB.
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Yazoubov, P., Kroug, M., Merkel, H., Kollberg, E., Gol'tsman, G., Lipatov, A., et al. (1998). Quasioptical NbN phonon-cooled hot electron bolometric mixers with low optimal local oscillator power. In Proc. 9th Int. Symp. Space Terahertz Technol. (pp. 131–140).
Abstract: In this paper, the noise perform.ance of NIN based phonon-cooled Hot Electron Bolometric (HEB) quasioptical mixers is investigated in the 0.55-1.1 THz frequency range. The best results of the DSB noise temperature are: 500 K at 640 GHz, 600 K at 750 GHz, 850 K at 910 GHz and 1250 K at 1.1 THz. The water vapor in the signal path causes a significant contribution to the measured noise temperature around 1.1 THz. The required LO power is typically about 60 nW. The frequency response of the spiral antenna+lens system is measured using a Fourier Transform Spectrometer with the HEB operating in a detector mode.
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Uzawa, Y., Miki, S., Wang, Z., Kawakami, A., Kroug, M., Yagoubov, P., et al. (2002). Performance of a quasi-optical NbN hot-electron bolometric mixer at terahertz frequencies. Supercond. Sci. Technol., 15(1), 141–145.
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